The present invention relates to an object-identification system in which moving or fixed objects, bearing characteristic codes, pass a device comprising means for remotely identifying these objects by reading their code.
An important application of our invention is in the identification of land vehicles, in particular motor cars, which in this case are fitted with a carrier member or support bearing the code that identifies the vehicles and is deciphered by detecting and processing the light radiation which the member reflects when subjected to illumination from a light source.
Thus, the identification device is of the opto-electrical type inasmuch as the information carried by the support associated with the object to be identified is picked up by optical means and its subsequent processing is performed by electrical or electronic means. In general terms, with such devices the illuminated object to be identified, (or that portion of it which carries) the characteristic information reflects part of the impinging light energy, now modulated by the code, to a detector which picks it up and transmits it to an electrically operated decoder. Devices of this nature are known and have already been constructed in practical form. In certain of these conventional devices, the light source employed is a laser emitting a fine single-color beam which illuminates the information carrier. The system used to displace the light beam is generally a rotating mirror drum which transmits incident light energy to the carrier and which transmits the energy reflected by the latter to an opto-electrical transducer of the photomultiplier type. Such devices obviously have the advantage of a good signal-to-noise ratio, chiefly as a result of the narrowness of the laser spectrum, but nonetheless they have some disadvantages, in particular the fact that the light beam is swept mechanically and that the laser ages when in a state of inactivity, aside from their high cost. It is possible to use a focused light source in lieu of a laser, but the mirror drum is still needed.
Another type of identification device is constructed around a television camera. The illuminating light source is then an incandescent lamp. Such a device has the advantages that it contains no mechanical moving parts, that it is small in size, and that its manufacturing cost is acceptable, but its low performance, its poor signal-to-noise ratio and the very large amount of light it requires make its use not very attractive.